The genus Thulinius has a very conserved morphology and its members are extremely similar to one another. Specimens of this genus should be very carefully examined, especially with regard to the presence or absence of lunules, which are sometimes barely visible especially in specimens in poor condition or in specimens with unsuitable orientation.

4 Basal claw very long and thin, cuticular bar under claws thin and short, evident subdivided lobes around the mouth ....................................................................................................................................................................... T. augusti

- Basal claw short and robust, cuticular bar under claws long and wide, absence of subdivided lobes around the mouth. ....................................................................................................................................................... T. stephaniae